Besides screen size, the resolution is another relevant spec to consider. 4K, also called UHD or 2160p, is the highest of the most common resolutions in monitors and televisions. It is precisely 3,840 pixels wide and 2,160 pixels tall and gives you four times the picture quality of 1080p.
In terms of resolution, usually bigger is better. The more pixels a screen has, the sharper the displayed image is. As a tradeoff, higher resolutions require more power from the source to drive all those pixels. Due to this tradeoff, 2K monitors became very popular with PC gamers.
Video game consoles work a little different; they are highly optimized systems designed for a specific target resolution. All current-generation consoles offer support for 4K games, and next-gen ones are specifically designed to run at 4K or above. If you also consider the vast amount of 4K video content available, it seems like buying a UHD display is a safe bet and a future-proof investment.